Electrically heated exhaust gas control apparatus

ABSTRACT

An electrically heated exhaust gas control apparatus includes: a hollow base member that has electroconductivity; a first insulation member that is disposed within the base member and that divides a vertically upper space and a vertically lower space from each other; a honeycomb catalyst formed in each of the vertically upper space and the vertically lower space; a pair of upper electrodes that heat the honeycomb catalyst in the vertically upper space and a pair of lower electrodes that heat the honeycomb catalyst in the vertically lower space; and a control portion that is able to stop electrifying the lower electrodes while continuing to electrify the upper electrodes.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2010-114305 filed on May 18, 2010 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an electrically heated exhaust gas control apparatus mounted, for example, in a vehicle, for purifying exhaust gas. More particularly, the invention relates to an electrically heated exhaust gas control that removes undesirable substances from exhaust gas by electrically heating a catalyst.

2. Description of the Related Art

In many industrial fields, various efforts and approaches for reducing impacts on the environment are being made worldwide. In particular, in the automobile industry, developments to encourage widespread use of and provide further improved performances of so-called eco-friendly cars, such as hybrid vehicles, electric motor vehicles, etc., in addition to highly fuel-efficient gasoline engine vehicles, are being pursued on a daily basis.

In some internal combustion engine vehicles, the exhaust system for exhaust gas that connects the vehicle engine and the muffler is provided with an electrically heated exhaust gas control apparatus that converts exhaust gas, that is, removes undesirable substances from exhaust gas, by activating a catalyst through electrical heating during a low-temperature condition, besides converting exhaust gas during a normal temperature condition. In this electrically heated exhaust gas control apparatus (or electrically heated converter (EHC)), as is apparent from the structure of a honeycomb heater disclosed in, for example, Japanese Patent Application Publication No. 3-288525 (JP-A-3-288525), a pair of electrodes are mounted on a honeycomb catalyst. The apparatus heats the honeycomb catalyst by passing a current through the electrodes, that is, electrifying the electrodes, to increase the activity of the honeycomb catalyst so as to make harmless the exhaust gas that passes through the honeycomb catalyst.

The foregoing exhaust system is also equipped with an exhaust gas control apparatus that includes a three-way catalyst. For example, the exhaust gas that is not sufficiently converted by the electrically heated exhaust gas control apparatus is converted by the three-way catalytic control apparatus, so that converted exhaust gas will pass through a muffler that is made up of a sub-muffler, a main muffler, etc.

The temperature of the electrically heated catalyst during an early period of reaction is about 300° C. It is very important to efficiently heat the catalyst and bring the catalyst into a state where the catalyst can exhibit its performance, in a very short time before the exhaust gas produced when the engine is started is emitted.

The foregoing exhaust gas contains a large amount of water.

When the exhaust gas is cooled in a low-temperature region in a downstream-side portion of the exhaust system, the water vapor in the exhaust gas turns into condensed water. For example, during the traveling of the vehicle, the condensed water sometimes resides at a position of the sub-muffler and accumulates to as much as 1 liter or more. Then, when the vehicle brakes, the condensed water can sometimes flow back to the foregoing exhaust gas control apparatus or even to a start converter that is disposed further upstream.

In the related-art electrically heated exhaust gas control apparatus for example, Japanese Patent Application Publication No. 3-288525 (JP-A-3-288525), there has been a concern of the backflow of condensed water causing an electrical insulation failure of an electrode (electrical leakage), which can lead to a failure of electrification. A factor contributing to this concern is a structure in which the electrodes that constitute the related-art exhaust gas control apparatus for example, Japanese Patent Application Publication No. 3-288525 (JP-A-3-288525) are exposed to condensed water.

At the time of the foregoing electrical leakage, the electrical heating of the catalyst cannot be performed, so that, for example, at the time of starting the engine or braking the vehicle, the exhaust gas control through the use of the electrically heated catalyst cannot be expected at all. Therefore, to avoid this electrical leakage, it is conceivable to adopt an improvement in which the entire exhaust gas control system that includes the exhaust gas control apparatus is provided as a reduced-voltage system. However, for this improvement, the system needs to be newly installed as a separate system in the vehicle, which will increase the vehicle weight and may become a cause of a decline in fuel efficiency.

Since the production of condensed water from exhaust gas is inevitable, there is a demand for development of an apparatus that is able to heat an electrically heated type catalyst and therefore secure its performance of the exhaust gas control even when condensed water enters the exhaust gas control apparatus, by improving the structure of the exhaust gas control apparatus while allowing the production of condensed water and the backflow of condensed water into the exhaust gas control apparatus. The contents of JP-A-3-288525 are incorporated herein by reference in their entirety.

SUMMARY OF THE INVENTION

The invention relates to an electrically heated exhaust gas control apparatus, and provides an electrically heated exhaust gas control apparatus that is capable of electrification even when condensed water enters the exhaust gas control apparatus.

An aspect of the invention is an electrically heated exhaust gas control apparatus that includes: a hollow base member that has electroconductivity; a first insulation member that is disposed within the base member and that divides an upper space and a lower space from each other; a honeycomb catalyst formed in each of the upper space and the lower space;

a pair of upper electrodes that heat the honeycomb catalyst in the upper space; a pair of lower electrodes that heat the honeycomb catalyst in the lower space; and a control portion that is able to stop electrifying the lower electrodes while continuing to electrify the upper electrodes.

According to the foregoing aspect, the apparatus detects an overcurrent through the electrodes that correspond to the lower space, in which condensed water can gather, and stops electrifying the electrodes before electrical leakage occurs, and, at the same time, continues electrifying the electrodes of the upper space to continue heating the honeycomb catalyst so as to ensure performance of the exhaust gas control without a stop of the control.

Furthermore, heat generated by the electrodes of the upper space is transferred to the lower space via the electroconductive base member, and therefore quickly evaporates the condensed water having gathered in the lower space, so that the lower space turns back into a state in which electrification is possible.

Although the honeycomb catalyst is not particularly limited, the honeycomb catalyst has a structure which is made up of many lattice profiles of a substantially quadrangular or substantially hexagonal shape that are made of silicon carbide or an electroconductive metal, such as a stainless type metal or the like, and in which in each lattice profile, a catalyst metal, such as platinum, palladium, rhodium, etc., is dispersed and supported in a matrix support that contains alumina, zirconia, ceria, etc. as a main component, and an air hole through which exhaust gas passes is formed in a central portion of each lattice profile.

In the exhaust system in which the exhaust gas control apparatus is disposed, an engine, the exhaust gas control apparatus, a three-way catalyst, a sub-muffler, a main muffler, etc., may be disposed in that order.

Besides, the first insulation member that divides the interior of the base member into two spaces, that is, the upper and lower spaces, may be made of a ceramic material, a cement, a thermosetting or thermoplastic resin, etc.

The electrically heated exhaust gas control apparatus of this invention, as compared with the related-art exhaust gas control apparatuses for example, Japanese Patent Application Publication No. 3-288525 (JP-A-3-288525), has a very simple improved structure in which the interior space of the hollow base member is divided into at least two spaces, that is, an upper space and a lower space, and each space is provided with a pair of electrodes. Due to this simple improved structure, it is possible to secure performance of the exhaust gas control by ensuring the electrification of at least a portion of the honeycomb catalyst while allowing the production of condensed water and the backflow of condensed water into the exhaust gas control apparatus.

Incidentally, the position at which the first insulation member is disposed in the interior of the base member, that is, the volumes of the upper space and the lower space that change depending on that position, may be adjusted by taking into consideration all of the amount of condensed water that is expected to flow back in, the value of current that is required of the upper space in order to secure a certain minimum degree of performance of the exhaust gas control, the amount of heat transferred to the lower space which is determined by the foregoing value of current for the minimum degree of performance of the exhaust gas control, etc. Thus, examples of the configurations obtainable by such adjustment include a configuration in which the first insulation member is disposed in a middle position in the base member that has a substantially circular contour (along a diameter passing through the center point), a configuration in which the first insulation member is disposed above a horizontal center (the volume of the upper space is relatively small), a configuration in which the first insulation member is disposed below the horizontal center (the volume of the upper space is relatively large), etc.

Besides, in the foregoing aspect, the exhaust gas control apparatus may further include a second insulation member that is disposed at least in the lower space and divides the lower space into a plurality of divided spaces, and each of the divided spaces may be provide with a honeycomb catalyst and a pair of divided electrodes. In this construction, the divided electrodes constitute the lower electrodes. The expression “that is disposed at least in the lower space” is meant to cover a configuration in which the second insulation member is disposed in both the upper space and the lower space as well as a configuration in which the second insulation member is disposed in only the lower space.

Besides, the expression “a plurality of divided spaces” covers, for example, a configuration in which the lower space is divided by the second insulation member into two divided spaces, a configuration in which the lower space is divided by two or more insulation members into three or more divided spaces, etc.

Each of the divided spaces formed as described above may have honeycomb catalyst and pair of electrodes. For example, if in the configuration in which the lower space is divided by two second insulation members into three divided spaces, condensed water gathers only in the middle divided space and causes overcurrent therein, it is possible to stop electrifying only the electrodes of this divided space while electrifying the electrodes of the other two divided spaces to heat their honeycomb catalysts, and therefore it is possible to secure performance of exhaust gas control by using these honeycomb catalysts and the honeycomb catalyst of the upper space.

Furthermore, in the foregoing aspect, the electrically heated exhaust gas control apparatus may further include a sensor that measures a value of current that flows between the lower electrodes, and the control portion may receive a measured datum from the sensor, and if the measured datum exceeds a predetermined threshold current value, the control portion may perform an OFF control of stopping electrifying the lower electrodes that correspond to the measured datum, and may continue electrifying at least the upper electrodes.

For example, the lower electrodes, or the divided-space electrodes of the divided spaces formed by dividing the lower space may be provided with switching elements that are disposed in their circuits connected to an electric power source. Then, an arbitrary current value between the value of the current that flows in the normal electrification condition and an overcurrent value that can lead to electrical leakage may be set as a threshold current value. There may be provided a control mechanism in which, for example, if the control portion determines that a measured datum regarding the value of the current through the lower electrodes is greater than the threshold current value, the control portion sends an OFF command signal to the corresponding switching element so that the electrification of the lower electrodes is switched off.

Besides, during the OFF control of the electrification of the lower electrodes, the electrification of the upper electrodes is continued, so that the heating of the honeycomb catalyst that corresponds to the upper space is continued and therefore performance of the exhaust gas control is secured. Furthermore, heat generated at an upper location is transferred to a lower location via the base member, so that the condensed water having gathered in the lower space can be evaporated as quickly as possible and therefore the overcurrent state of the lower electrodes can be removed. Then, the electrification of the lower electrodes can be started again to recover the initial performance of the exhaust gas control.

According to the electrically heated exhaust gas control apparatus of the this aspect, due to an improved structure in which the hollow base member is divided into at least two spaces, that is, the upper and lower spaces, by the first insulation member, and each space is provided with a pair of electrodes, the following effects are achieved. That is, in the case where condensed water enters the apparatus and causes overcurrent in the lower space and therefore the electrification of the lower electrodes is stopped before electrical leakage occurs, the electrification of the upper electrodes, which are allowed to be electrified, is ensured. This in turn secures the heating of the honeycomb catalyst in the upper space and therefore continuous performance of the exhaust gas control. Besides, heat generated at an upper location is transferred to a lower location via the base member, so that the condensed water having gathered in the lower space can be quickly evaporated. When the overcurrent state of the lower electrodes is thus removed, the electrification of the lower electrodes can be started again, so that the initial performance of the exhaust gas control will be recovered.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, advantages, and technical and industrial significance of this invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a schematic diagram illustrating an exhaust system for exhaust gas which includes an exhaust gas control apparatus in accordance with an embodiment of the present invention;

FIG. 2A is a schematic diagram illustrating an embodiment of the exhaust gas control apparatus of the present invention, and FIG. 2B is an enlarged view of a portion b shown in FIG. 2A;

FIG. 3 is a schematic diagram illustrating another embodiment of the exhaust gas control apparatus of the present invention;

FIG. 4A to FIG. 4F are schematic diagrams illustrating various configurations of division of an interior of a base member according to the present invention;

FIG. 5 is a control flowchart for the exhaust gas control apparatus shown in FIG. 2A; and

FIG. 6 is a control flowchart for the exhaust gas control apparatus shown in FIG. 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

An electrically heated exhaust gas control apparatus 200 of an embodiment of the present invention is disposed in an exhaust system shown in FIG. 1. This exhaust system includes an engine 100, an exhaust gas control apparatus 200, a three-way catalyst exhaust control apparatus 300, a sub-muffler 400, and a main muffler 500. The exhaust gas produced in the engine 100 is discharged in a direction X1 shown in FIG. 1.

In the exhaust system shown in FIG. 1, a honeycomb catalyst that constitutes the exhaust gas control apparatus 200 is quickly heated to a predetermined temperature, for example, when the engine 100 is started. Then, it is important to effectively convert exhaust gas flowing from the engine with the honeycomb catalyst. If the exhaust gas cannot be sufficiently converted by the exhaust gas control apparatus 200, the exhaust gas is further converted by the three-way catalyst exhaust control apparatus 300, which is disposed downstream of the exhaust gas control apparatus 200.

The electrically heated exhaust gas control apparatus 200 includes an exhaust control apparatus main body 10, a control portion 20, and an electric power source 30 that supplies electricity to the exhaust control apparatus main body 10, that is, electrifies the exhaust control apparatus main body 10.

The form of an embodiment of the exhaust gas control apparatus will be described with reference to FIG. 2 and FIG. 3 in that order.

The exhaust control apparatus main body 10 constituting the electrically heated exhaust gas control apparatus 200 shown in FIG. 2 includes: an electroconductive hollow base member 1; a first insulation member 5 disposed in a hollow interior 1 a of the hollow base member 1; honeycomb catalysts 2A and 2B disposed in an upper space 1 a 1 and a lower space 1 a 2, respectively, in the interior 1 a that are divided from each other by the first insulation member 5 and are formed on an upper side and a lower side, in a vertical direction, of the insulation member 5; a pair of electrodes 3A for heating the honeycomb catalyst 2A disposed in the upper space 1 a 1; and a pair of electrodes 3B for heating the honeycomb catalyst 2B disposed in the lower space 1 a 2. Incidentally, as for the electrodes 3A and 3B, root portions of circuit lines thereof are covered with insulation covers 3Aa and 3Ba that are provided for preventing shortcircuit. Besides, although not shown in the drawings, the base member 1 is housed in a converter case (not shown), and a damper mat or the like (not shown) may be interposed at contact portions between the converter case and the base member 1. Incidentally, the first insulation member 5 may be an insulation member that extends horizontally.

The base member 1 is made of silicon carbide, or of an electroconductive metal such as a stainless type metal or the like. Many lattice profiles that constitute the honeycomb catalysts 2A and 2B within the base member 1 may also be formed from an electroconductive material that is the same as or similar to the electroconductive material of the base member 1.

The honeycomb catalyst 2A (and the honeycomb catalyst 2B as well), as shown in FIG. 2B, is made up of many substantially quadrangular lattice profiles 2Aa that are made of silicon carbide, or an electroconductive metal such as a stainless type metal or the like. In each lattice profile, there is formed a catalyst layer 2Ab in which a catalyst metal, such as platinum, palladium, rhodium, etc., is dispersed and supported in a matrix support that contains alumina, zirconia, ceria, etc. as a main component. Inside the catalyst layer 2Ab, there is formed at least an air hole 2Ac through which exhaust gas passes.

The first insulation member 5 that divides the interior 1 a of the base member 1 into the two spaces, that is, the upper and lower spaces, is formed from a ceramic material, a cement, a thermosetting or thermo-plastic resin, etc.

When the electrodes 3A and 3B of the base member 1 are electrified, current flows from the electroconductive base member 1 to the lattice profiles 2Aa, so that the catalyst layer 2Ab is heated to an increased temperature and therefore the activity of the catalyst is increased.

The honeycomb catalyst 2A in the upper space and the honeycomb catalyst 2B in the lower space are provided with the electrodes 3A and the electrodes 3B, respectively. Of these electrodes, the positive electrodes are interconnected and the negative electrodes are interconnected so as to form a parallel circuit 4 that is electrically connected to the electric power source 30.

Therefore, in the case where condensed water collects in the lower space and causes an overcurrent that is larger than a current that flows in a normal condition of electrification, so that the electrification of the electrodes 3B of the lower space is stopped before electrical leakage occurs, it is still possible to continue the electrification of the electrodes 3A of the upper space, which are independent of the electrodes 3B. Then, heat generated by increasing the temperature of an upper region in the base member 1 that is caused by the electrification of the electrodes 3A is transferred to a lower region in the base member 1. This heat evaporates the condensed water having gathered in the lower space 1 a 2, and therefore removes the state of overcurrent, so that the electrification of the electrodes 3B of the lower space can be started again.

Detection of the foregoing overcurrent state occurring in the circuit of the electrodes of the lower space, and an electrification stop control performed at that time will be described below.

The electrode circuit of the lower space is provided with an electric current sensor 7 and a switching element 6 as shown in FIG. 2A.

The current sensor 7 and the switching element 6 are both connected to the control portion 20.

A detailed illustration of the construction within the control portion 20 is omitted. The control portion 20 contains an interface to which measured data regarding the value of the current from the current sensor 7 are input, a storage portion in which a predetermined threshold current value datum is stored, a comparison operation portion that compares the measured data with the threshold current value datum, a signal sending portion that sends an OFF control signal to the switching element 6 when a measured datum is greater than the threshold current value datum, and a CPU that governs the operations of these portions, as well as a RAM, a ROM, a bus that connects the foregoing components, etc.

For example, if condensed water flows back from the sub-muffler 400 side, and enters the exhaust control apparatus main body 10 and, in particular, the lower space 1 a 2, and accumulates to a predetermined amount, an overcurrent flows in the circuit. In the storage portion of the control portion 20, an arbitrary value of current between the value of the current that flows in the normal electrification condition and an overcurrent value that can result in electrical leakage is pre-stored as a threshold current value.

The current sensor 7 always measures the value of the current that flows though the circuit of the electrodes 3B. When an overcurrent flows in the electrode circuit of the lower space and the current sensor 7 sends a measured datum regarding the overcurrent to the control portion 20, the control portion 20 sends an OFF signal to the switching element 6 in order to stop the electrification of the circuit of the electrodes 3B. The stop of the electrification effectively restrains electrical leakage between the electrodes.

An exhaust control apparatus main body 10A of an exhaust gas control apparatus 200A shown in FIG. 3 has a total of four divided spaces 1 a 1′ and 1 a 2′ that are formed by dividing an interior 1 a of a base member 1 by a first insulation member 5 and a second insulation member 8 so that an upper space and a lower space divided by the first insulation member 5 are each divided into two spaces by the second insulation member 8.

Incidentally, the second insulation member may instead by an insulation member that extends vertically.

Each of the four divided spaces 1 a 1′ and 1 a 2′ is provided with a pair of electrodes 3A1 or 3B1 by disposing an electrode on one of two opposite sides of the second insulation member 8 so that the electrode lies opposite and thus pairs with a corresponding one of four electrodes 3A1 and 3B1 that are disposed on a surface of the base member 1.

Furthermore, each one of electrode circuits that correspond one-to-one to the divided spaces 1 a 1′ and 1 a 2′ is provided with a current sensor 7 and a switching element 6 that are connected to the control portion 20 so that data can be sent and received therebetween. According to this exhaust control apparatus main body 10A, in the case where an overcurrent is flowing through only one of the left and right lower spaces, or the case where an overcurrent is flowing through one of the left and right divided spaces of the upper space as well as the lower spaces, it is possible to stop the electrification of the electrode circuit of the one or more spaces through which the overcurrent is flowing. Thus, the exhaust control apparatus main body 10A enables finer control than the exhaust control apparatus main body 10.

Incidentally, each of the exhaust control apparatus main body 10 and the exhaust control apparatus main body 10A has its own advantages. As for the exhaust control apparatus main body 10, in which the interior of the base member is divided into only two spaces, that is, the upper and lower spaces, this small number of the divided spaces requires only correspondingly small numbers of switching elements and current sensors, and therefore the computation load on the control portion is correspondingly less. On the other hand, as for the exhaust control apparatus main body 10A, in which the interior of the base member is divided into four spaces, it is possible to more finely sort areas within the base member which are appropriate to continue to electrify.

FIGS. 4A to 4F show examples of various configurations of division of the interior of the base member according to the embodiment of the present invention, each showing only the profile of the base member 1 and the first insulation member 5 and, in some of the examples, the second insulation member 8, while omitting the illustration of the honeycomb catalyst. Although the contour of the base member 1 is substantially circular, it is also possible to set various contours other than the circular contour for the base member 1 as desired in relation with the space for installation or with other appliances, for example, as a substantially ellipse, a substantially quadrangle, a substantially square, other substantially polygons, etc.

FIG. 4A shows a configuration of the base member shown in FIG. 2A. FIG. 4F shows the base member shown in FIG. 3. FIG. 4A shows a configuration of the base member in which the upper space 1 a 1 and the lower space 1 a 2 are divided from each other by the first insulation member 5 that extends through the center O of the circle, and therefore have equal areas and equal volumes. FIG. 4F shows a configuration of the base member in which the left and right upper spaces 1 a 1′ and the left and right lower spaces 1 a 2′ are divided from each other by the first insulation member 5 and the second insulation member 8 that extend through the circle center O, and therefore have equal areas and equal volumes.

The base member show in FIG. 4B has a configuration in which the first insulation member 5 is disposed above the circle center O, and therefore the volume of the upper space 1 a 1 is relatively small. The base member show in FIG. 4C has a configuration in which the first insulation member 5 is disposed below the circle center O, and therefore the volume of the upper space 1 a 1 is relatively large.

The foregoing position at which the first insulation member 5 is disposed may be adjusted by factoring in the amount of condensed water that is expected to flow back in, the value of current that is required of the upper space in order to secure a certain minimum degree of performance of the exhaust gas control, the amount of heat transferred to the lower space which is determined by the foregoing value of current for the minimum degree of performance of the exhaust gas control, etc.

The base member shown in FIG. 4D has a configuration based on the configuration shown in FIG. 4A in which the lower space is divided into two divided spaces 1 a 2′ by a second insulation member 8 that extends from the circle center O in the form of a radius. The base member shown in FIG. 4E has a configuration based on the configuration show in FIG. 4A in which the lower space is divided into three divided spaces 1 a 2″ by two second insulation members 8.

Next, control methods employed by the control portion to measure the overcurrent and determine whether or not to stop the electrification on the basis of the measured data of the overcurrent will be briefly described with reference to a control flowchart for the electrically heated exhaust gas control apparatus 200 shown in FIG. 5, and a control flowchart for the electrically heated exhaust gas control apparatus 200A shown in FIG. 6.

Firstly, with regard to the control method of the electrically heated exhaust gas control apparatus 200 that determines whether or not to electrify the electrode circuit of the lower space, after the engine is started (step S1 in FIG. 5), the electrification of the upper electrodes and the lower electrodes is started, and the value of the current through the lower electrodes is measured by the current sensor, and the measured datum is sent to the control portion 20 at appropriate timing (step S2).

The measured datum from the current sensor is compared with the threshold current value pre-stored in the storage portion provided in the control portion 20 as described below, by the comparison operation portion (step S3).

The threshold current value is set at a predetermined current value which is larger than the current value that occurs during normal electrification and which can result in electrical leakage. If the measured datum is smaller than the threshold current value, it is considered that there is no possibility of electrical leakage regarding the electrode circuit of the lower space, and the electrification of the lower electrodes and the upper electrodes is continued for a predetermined time (step S4).

On the other hand, if the measured datum is greater than the threshold current value, it is considered that the electrode circuit of the lower space has a possibility of electrical leakage, and therefore only the electrification of the lower electrodes is stopped (step S5). Then, after a predetermined time elapses, the comparison of a measured datum of the current value with the threshold current value is executed again (step S6). If during the time from step S5 to step S6, heat generated by the upper electrodes is transferred to a lower portion of the base member via the base member, and evaporates the condensed water having gathered in the lower space, so that the overcurrent state of the lower electrodes is removed, the determination in step S6 provides a result that the presently measured datum is smaller than the threshold current value. In this case, the process returns to step S2, and proceeds to step S3, and then to step S4, in which the electrification of the upper electrodes and the lower electrodes is started again.

Incidentally, in the case where if the routine is repeated a plurality of times, the state in which the presently measured datum is greater than the threshold current value still remains, it may be determined that electrical leakage is occurring at a site other than the lower electrode circuit, or that the lower space is flooded with a large amount of condensed water that cannot be evaporated, or the like, and then a system fault may be warned of.

Besides, although not shown in the drawings, a control mechanism may also be provided in which a thermocouple is disposed in the exhaust control apparatus main body 10, and the base member temperature in the lower space of the base member 1 is periodically measured by the thermocouple, and the measured temperature datum is sent to the control portion. With this mechanism, it is possible to apply a control method in which a threshold temperature value is provided for the temperature of the base member 1, and step S4 is followed by a further step of comparing the base member temperature in the lower space and the threshold temperature value, and if the base member temperature is higher than or equal to the threshold temperature value, the electrification is ended, and if the base member temperature is lower than the threshold temperature value, the process returns to step S4 in order to continue the electrification of the upper electrodes and the lower electrodes.

The control flow of the electrically heated exhaust gas control apparatus 200A shown in FIG. 6 is different from the control flow shown in FIG. 5 in the respect that the electrode circuits to be controlled are all the four electrode circuits that correspond to the four divided spaces (steps S2 to S6 in FIG. 5 correspond to steps S2′ to S6′ in FIG. 6).

According to either one of the electrically heated exhaust gas control apparatuses 200 and 200A of the foregoing embodiments, if condensed water flows back into the exhaust control apparatus main body 10 or 10A that constitutes the exhaust gas control apparatus, the electrical leakage from any one of the electrode circuit due to the condensed water will be avoided, and the heating of at least a portion of the honeycomb catalyst will be continued so as to continue the exhaust gas control. Furthermore, heat from the electrode circuit that continues being electrified is transferred via the base member to a circuit region whose electrification has been stopped, so that the condensed water therein will be quickly evaporated and the electrification of the circuit that has stopped being electrified can be started again.

While the embodiments of the present invention have been described above in detail with reference to the drawings, concrete constructions of the invention are not limited to what have been disclosed above in conjunction with the embodiments, and changes in design and the like made without departing from the gist of the invention are also included within the present invention. 

1. An electrically heated exhaust gas control apparatus comprising: a hollow base member that has electroconductivity; a first insulation member that is disposed within the base member and that divides an upper space and a lower space from each other; a honeycomb catalyst formed in each of the upper space and the lower space; a pair of upper electrodes that heat the honeycomb catalyst in the upper space; a pair of lower electrodes that heat the honeycomb catalyst in the lower space; and a control portion that is able to stop electrifying the lower electrodes while continuing to electrify the upper electrodes.
 2. The electrically heated exhaust gas control apparatus according to claim 1, wherein the first insulation member is made of one of a ceramic material, a cement, a thermosetting resin, and a thermoplastic resin.
 3. The electrically heated exhaust gas control apparatus according to claim 1, wherein the first insulation member is disposed at a middle position in the base member.
 4. The electrically heated exhaust gas control apparatus according to claim 1, wherein the first insulation member is disposed above a horizontal center of the base member.
 5. The electrically heated exhaust gas control apparatus according to claim 1, wherein the first insulation member is disposed below a horizontal center of the base member.
 6. The electrically heated exhaust gas control apparatus according to claim 1, further comprising: a second insulation member that is disposed at least in the lower space and divides the lower space into a plurality of divided spaces; and a honeycomb catalyst and a pair of divided electrodes that are provided specifically for each of the divided spaces.
 7. The electrically heated exhaust gas control apparatus according to claim 6, wherein the second insulation member is disposed in both the upper space and the lower space.
 8. The electrically heated exhaust gas control apparatus according to claim 1, further comprising a sensor that measures a value of current that flows between the lower electrodes, wherein the control portion receives a measured datum from the sensor, and if the measured datum exceeds a predetermined threshold current value, the control portion performs an OFF control of stopping electrifying the lower electrodes that correspond to the measured datum, and continues electrifying at least the upper electrodes.
 9. The electrically heated exhaust gas control apparatus according to claim 6, further comprising a sensor that measures a value of current that flows between the divided-space electrodes of each divided space of the lower space, wherein the control portion receives measured data from the sensor, and if a measured datum of the measured data from the sensor exceeds a predetermined threshold current value, the control portion performs an OFF control of stopping electrifying the divided-space electrodes that correspond to the measured datum, and continues electrifying at least the upper electrodes.
 10. The electrically heated exhaust gas control apparatus according to claim 1, further comprising a thermocouple that is disposed in an exhaust control apparatus main body and that periodically measures base member temperature in the lower space of the base member, and sends the base member temperature to the control portion, wherein the control portion determines whether or not the base member temperature in the lower space is higher than or equal to a threshold value, and if the base member temperature is higher than or equal to the threshold temperature value, the control portion ends electrification of the lower electrodes, and if the base member temperature is lower than the threshold temperature value, the control portion continues electrifying the upper electrodes and the lower electrodes.
 11. The electrically heated exhaust gas control apparatus according to claim 6, further comprising a thermocouple that is disposed in an exhaust control apparatus main body and that periodically measures base member temperature in the lower space of the base member, and sends the base member temperature to the control portion, wherein the control portion determines whether or not the base member temperature in the lower space is higher than or equal to a threshold value, and if the base member temperature is higher than or equal to the threshold temperature value, the control portion ends electrification of the lower electrodes, and if the base member temperature is lower than the threshold temperature value, the control portion continues electrifying the upper electrodes and the lower electrodes.
 12. The electrically heated exhaust gas control apparatus according to claim 8, further comprising a thermocouple that is disposed in an exhaust control apparatus main body and that periodically measures base member temperature in the lower space of the base member, and sends the base member temperature to the control portion, wherein the control portion determines whether or not the base member temperature in the lower space is higher than or equal to a threshold value, and if the base member temperature is higher than or equal to the threshold temperature value, the control portion ends electrification of the lower electrodes, and if the base member temperature is lower than the threshold temperature value, the control portion continues electrifying the upper electrodes and the lower electrodes. 